初应力状态下夹芯复合材料曲梁面板的局部振动的理论分析

在船舶领域,以复合材料层合面板及泡沫芯材组成的夹芯复合材料板梁结构已大量应用在游艇及复合材料高速艇上.文章研究了受初始静载荷作用下夹芯复合材料曲梁的面板的局部自由振动问题,并给出一种相应的理论分析方法.文中通过将芯材简化为Winkler弹性地基,将面板简化为一复合材料曲梁,从而使所研究问题蜕化为有初始静载荷作用下弹性地基上任意曲梁的固有振动问题.在局部振动位移是基于初始静载平衡位置并与初始位移相比是小量的假定的基础上,根据能量原理推导出面板的运动方程.研究的结果表明,该面板的局部振动不只取决于面板的弯曲刚度和长度,以及芯材的弹性刚度,也在很大程度上取决于梁的曲率及面板所受到的初始轴向压力.     

Design and development of a stated choice experiment for interdependent agents: accounting for interactions between buyers and sellers of urban freight services

Stated choice experiments have proven to be a powerful tool in eliciting preferences across a broad range of choice settings. This paper outlines the elements of a group-based experiment designed for interdependent urban freight stakeholders, along with the procedure to administer the questionnaire sequentially. The focus is on the design of a computer-assisted personal survey instrument and the value in disseminating the details of a new approach to design and collect stated choice data for interacting agents. The paper also discusses how to specify a reference alternative, and then how to recruit appropriate real-market or representative decision-making group members to participate in a subsequent phase of the survey, which incorporates the reference alternative and contextual information from an initial phase. The empirical strategy, set out in some detail, provides a new framework within which to understand more fully the role that specific attributes, such as variable user charges, influencing freight distribution chains might play, and who in the supply chain is affected by specific attributes in terms of willingness to pay for the gains in distribution efficiency.

Entry barriers in seaports

The different types of entry barrier in seaports are analysed and the policies and practices to reduce them are discussed in this paper. In most seaports, economic, regulatory, and geographical entry barriers are substantial and increasing in complexity as ports become embedded in supply chains and multilayered networks with multiple entry-levels. Various entry barriers in seaports are identified through an overview of the relevant literature and their presence is confirmed by empirical data describing them. The case is then made for lowering these barriers. This would be desirable from an economic point of view, since lower barriers strengthen the contestability of markets and increase the level of intra-port competition. The latter might yield substantial benefits, such as fostering specialization and preventing the abuse of market power. Finally, low entry barriers would facilitate the faster implementation of new technologies and business models. In the third part of the analysis, policies and practices designed to reduce entry barriers are examined. The implications are discussed of current national and supranational (EU) policy initiatives aimed to liberalize service provision in seaports. Other (de)regulatory policies that could contribute to the reduction of entry barriers are analysed.     

Effect of fuel choice on nanoparticle emission factors in LPG-gasoline bi-fuel vehicles

Nanoparticle and gas-phase emission factors are presented for a liquefied petroleum gas (LPG) passenger vehicle and are compared to gasoline operation. A bi-fuel LPG-gasoline vehicle certified for use on either fuel was used as the test vehicle so that a direct comparison of the emissions could be made based on fuel choice. These values were considered along with previous studies to determine the relative change in particulate emissions due to fuel choice over a wide range of vehicles and operating conditions. The vehicle examined in this study was tested on a chassis dynamometer for both steadystate and transient conditions. Transient test cycles included the US FTP72 driving cycle, Japanese driving cycle and modified Indian driving cycle while steady-state tests were done at vehicle speeds ranging from 10–90 km/hr in various transmission gears. Exhaust particle size distributions were measured in real-time using a differential mobility spectrometer (DMS50), and particle number and particle mass emission factors were calculated. For both fuels, the majority of the particles ranged from 5 to 160 nm in terms of particle diameter, with typically more than 85% of the particles in the nucleation mode (between 5–50 nm). In most cases, the vehicle produced a greater fraction of larger (accumulation mode) particles when fuelled on LPG. Using the data in the literature as well as the data in the current study, gasoline fuel produces 4.6 times more particles in terms of number and 2.1 times more particles in terms of mass.     

用超声波检测评定焊缝的不连续性

用超声波检测,根据测试的灵敏度,可获得焊缝不连续性的6个基本方面:(1)与标准反射物的回波信号相比较,从试样的反射波幅的大小可以近似地估计反射区的大小.     

Changing ownership structures in the Dutch fleet

The new Dutch shipping policy has given rise to high expectation and curiosity in the world of shipping. This, together with the obvious difficulties of an ex-post study of the effectiveness of such innovative policy, has prompted the authors to take an interest in attempting to investigate changes in ownership of the Dutch fleet 2 years after the new policy has been introduced. To do this, a rather new concept of 'flagging out' has been adopted, which is interpreted as a process leading to different degrees of 'foreignness' in a shipping operation. In this paper, a method to structure is presented, and ownership information, and changes in it are presented, that are essentially based on the theory of stochastic processes. The data used is the Dutch fleet data, which includes information on the nationality of the flag, parent ownership and management over the period 1994-1998. The results yield interesting insights in the shifts in the ownership and operational structure of shipping companies induced by the new policy. In particular, they allow one to establish the origin of new vessels, in which stage of ownership/operation it is most likely that shifts occur, and to determine the relationship between the different stages of the 'flagging out' process. These results, thus, enable an evaluation of the areas in which the policy can be expected to yield results.     

Risk management methods for the liner shipping industry: the case of the Bunker Adjustment Factor

Through the implementation of the Bunker Adjustment Factor (BAF), a shipowner is able to transfer the risk of fuel price fluctuation to the shipper. This and other surcharges are generally undesired by shippers who must pay this fee. The research presented provides an alternative method of risk management that is more effective than the current method, while responding to customer service demands for simplified tariffs. By strategic use of commodity futures, the shipowner is able to better reduce his/her risk exposure, transferring it to willing parties at the futures exchanges, thereby eliminating the need for the bunker surcharge.     

Options-Based Multi-Objective Evaluation of Product Platforms

A platform is the set of elements and interfaces that are common to a family of products. Design teams must choose among feasible platform concepts upon which a product family could be based, often involving new technologies. Multiple performance objectives need to be considered. A standard approach is to convert the performance outcomes into financial figures, which can then be weighed against the required investments. However, it is not always possible to transform performance outcomes (benefits) into monetary terms, such as in defense or highly technical projects. A multi-objective form of real-options-based platform selection is developed. Systems are compared based on multiple technical and economic goals, incorporating uncertainty by representing the unknown factors during the subsequent development process with probability distributions. The range of uncertain outcomes is integrated into single expected measures of effectiveness, which can then be applied to select the most appropriate platform and set of support product variants. An application to the design of platform-based families of naval high-speed ships is shown.     

The role of cities in achieving the EU targets on biofuels for transportation: The cases of Berlin,London, Milan and Helsinki

Road transportation is a strongly growing source of CO₂, and use of biofuels represents one option to reduce end-of-pipe emissions of the existing car fleet. In this contribution, the implementation of the EU Biofuels Directive (2003/30/EC) and related voluntary measures at the local level are examined in Germany, UK, Italy and Finland and the cities of Berlin, London, Milan and Helsinki. Even though they are not directly involved in the implementation of the biofuel directive, all four cities studied have played an important role in emissions reduction by voluntarily participating in research and demonstration projects and by using biofuels in their own fleet. An analysis of the numerous causes and driving forces leading to different local level measures is provided. The environmental sensitivity, usually examined at national level, and the national level implementation of the EU Biofuels Directive (2003/30/EC) were not directly correlated with the city-level activities Instead, support from local businesses and acquisition of EU funds were considered to be valid explanatory factors for the city-level activities. In addition, through horizontal networking cities are starting to exchange know-how gained in their projects, contributing in this way to the accumulation of experience for future policies and technologies.     

A return period based plastic design approach for ice loaded side-shell/bow structures

Based on the design ice load that corresponds to a certain return period, a practical approach for designing the frames behind the side-shell or the bow of a ship subject to ice loading is proposed. Four typical types of section profiles have been selected for modelling and numerical analysis. Non-linear finite element analyses that involve both the geometric and material non-linearity were performed. From the analyses, the relationships between the loads and the beam's cross-section properties were obtained for different permanent set requirements. These relationships were then used for finding the section modulus from which the cross-section of the beam can be decided. Finally, a design example is presented for illustration.